In recent years, mobile communication systems such as land mobile radio telephone, portable telephone and personal handy phone system (referred to as a PHS hereinafter) have been put into practical use and are rapidly gaining popularity. For the compacting and power saving of the wireless mobile terminal (referred to as a mobile terminal hereinafter), the effective use of radio waves and the other purposes, the radio zones of these mobile communication systems are distributed into ranges of micro-cells and pico-cells, which are smaller than in the conventional case.
In the mobile communication system, a line setting for communications is executed on a mobile terminal from a communication line network, thereby achieving a call. For this purpose, the registration and management of calling areas of the mobile terminal are executed. In the above-mentioned systems using micro-cells and pico-cells, it is proposed to utilize a calling area registering operation of a mobile terminal for specifying the position of the mobile terminal, taking advantage of such feature that each radio zone is small.
An example of the specifying of the position of a mobile terminal in the case of the PHS will be described below.
FIG. 7 shows a construction of a PHS public service system. FIG. 8 shows a construction of a physical slot for controlling a control channel. FIG. 9 shows an operation flow at the time of registering a calling area of a mobile terminal.
In FIG. 7, 71 denotes a mobile terminal;
72a, 72b, 72c, . . . denote base stations for executing speech call communications and registration of calling areas together with the mobile terminal 71,
73a, 73b, 73c, . . . denote radio zones of the base stations 72a, 72b, . . . , respectively;
74 denotes a general calling area comprised of a plurality of above-mentioned radio zones 73a, 73b, . . . ; and
75 denotes a control station for executing control of line connection to the mobile terminal 71 located inside the general calling area 74.
The base stations 72a, 72b, 72c, . . . are connected to one another through the control station 75 and the telecommunication line equipments 76a, 76b, 76c, . . . .
The base stations 72a, 72b, 72c, . . . periodically transmit a signal including a general calling area number 77 of the control station 75, using a control slot shown in FIG. 8, so as to execute call connection with the mobile terminal 71.
FIG. 8 shows a construction of a physical slot for controlling the control channel of the PHS public system, where the general calling area number 77 is included in an outgoing identification code section shown in the figure.
The base stations 72a, 72b, 72c, . . . managed by the control station 75 transmit an identical general calling area number 77 and transmit base station identification information that differ depending on each base station.
The control stations of adjacent general calling areas transmit different general calling area numbers. The mobile terminal 71 detects the change of the general calling area number and registers the calling area in the control station via the base station.
In the operation flow of FIG. 9, the mobile terminal 71 establishes a synchronism with a signal from a base station which received a signal at the maximum intensity of electric field in a "control channel selection" state after turning on the power, and transfers to a "waiting" state with the recognition of "channel selection OK" when the base station can be used. When no synchronism can be established with the base station or when the base station cannot be used, the control channel selection is executed again.
In the "waiting" state, the general calling area number transmitted from the currently receiving base station is compared with the general calling area number when the mobile terminal has executed the registration of the calling area at the preceding time, and when the numbers are different from each other, the calling area is registered in the control station that controls the base station.
Further, in the "waiting" state, a difference between the retention level of the intensity of electric field of waiting and the level of the intensity of received electric field is watched, thereby making a decision on radio zone transfer and zone transfer between general calling areas (change of registration of calling area).
If the level of the intensity of received electric field is lower than the retention level of the intensity of electric field for waiting, then a transfer to the "control channel selection" state is effected, and a synchronism is established with the signal from the new base station which received a signal at the maximum intensity of electric field, thereby effecting a transfer to the "waiting state". In the "waiting state", the general calling area number transmitted from the currently receiving base station is compared with the general calling area number when the mobile terminal has executed the registration of the calling area at the preceding time, and when the numbers are different from each other, the calling area is newly registered in the control station that controls the base station similar to the above-mentioned case.
As described above, the mobile terminal executes the calling area registration, and the control station detects that the mobile terminal is located inside the calling area of the station itself.
Since the positional information (geographical information) of the calling area that each control station manages has been already known, the current position of the mobile terminal registered in the control station is subordinately specified.
However, with the above-mentioned construction, the mobile terminal does not execute position registration until the general calling area number changes, and therefore, the locating or positional specifying of the mobile terminal can only be executed in the unit of each general calling area comprised of a plurality of radio zones. Therefore, the above-mentioned construction has been insufficient for such an application that requires locating or positional specifying of the current position of the mobile terminal with a high accuracy.